Potentiometer having a transport screw and diamond shaped contact spring

ABSTRACT

A potentiometer having a slide, comprising a diamond-shaped contact spring, which is rectilinearly displaceable by means of a transport screw spindle, one half of said contact spring cooperating with the screw spindle as a nut and pressing the slide onto a guide, the other half serving as a wiper.

United States Patent 1 91 Van Rooijen POTENTIOMETER HAVING A TRANSPORT SCREW AND DIAMOND SHAPED CONTACT SPRING Inventor:

Jan Van Rooijen, Emmasingel, Eindhoven, Netherlands Assignee: U.S. Phillips Corporation, New

York, N.Y.

Filed: Oct. 18, 1971 Appl. No.: 190,057

[30] Foreign Application Priority Data Oct. 20, 1970 Netherlands 7015318 US. Cl. 338/180, 338/22 Int. Cl HOlc 9/02 Field of Search 338/118, 160, 176,

[56] References Cited UNITED STATES PATENTS 3,518,605 6/1970 Kirkendall 338/180 X FOREIGN PATENTS OR APPLICATIONS 11/1970 Great Britain 338/180 1,035,521 7/1966 Great Britain 338/202 Primary ExaminerHerman J. Hohauser Assistant Examiner-Gerald P. Tolin Att0meyFrank R. Trifari [57] ABSTRACT A potentiometer having a slide, comprising a diamondshaped contact spring, which is rectilinearly displaceable by means of a transport screw spindle, one half of said contact spring cooperating with the screw spindle as a nut and pressing the slide onto a guide, the other half serving as a wiper.

4 Claims, 7 Drawing Figures Ill/III Ill POTENTIOMETER HAVING A TRANSPORT SCREW AND DIAMOND SHAPED CONTACT SPRING The invention relates to a potentiometer having a' slide, comprising a contact spring, which is rectilinearly displaceable in a trough-shaped housing by means of a transport screw spindle and which is guided by the inner walls of the trough and ridges provided thereon. A portion of the contact spring engages the screw thread electrically conducting spindle and acts as a nut and a contact. A second portion of the contact spring forms a wiper which is movable over a resistance track.

A known contact spring (for example from Netherlands Pat. application No. 6808170) is constructed as a U-shaped metal wire. If extremely high requirements are imposed as regards the adjusting accuracy of the potentiometer and the stability of the adjustment, also in the case of shocks and vibrations, the known construction cannot always meet these requirements.

The object of this invention is to provide a potentiometer meeting very severe requirements as regards adjusting accuracy and stability, its dimensions being equally small as those of the known device.

The potentiometer according to the invention is characterized in that each of the two portions of the contact spring consists of a substantially V-shaped leaf spring, the openings of the vees of said leaf springs facing each other so that a side elevation of the contact spring is approximately diamond-shaped with its longest dimension extending in the direction of that of the slide. The strip-shaped ends. of the nut portion of the contact spring keep the slide pressed against the guide ridges. The tip of the vee of the wiper portion engages the resistance track at a force which is smaller than that exerted by the nut portion on the screw spindle.

As the rather wide, strip-shaped ends of the nut portion bear on the slide, the slide, being arranged against the ridges such that it cannot be tilted, prevents tilting of the nut portion. Further, since the diamond shaped contact spring provides greater rigidity in the direction of transport a major source of backlash upon adjustment is eliminated. As the slide is continuously pressed onto the ridge by the nut portion, the engaging pressure of the wiper portion is independent of the resilience of the nut portion, so that the wiper can always slide over the resistance track at the desired, predetermined pressure.

It is to be noted that British Pat. specification No. 1,035,521 describes a contact spring for a potentiometer having a transport screw. This contact spring has two leaf spring portions, one portion of which acts as a nut and the other portion acts as a wiper. This contact spring, however, is not accommodated in a slide, but is guided in that portions of the spring itself extend along the side walls and over the top of the side walls of the potentiometer. In this case the metal of the spring might damage the synthetic resin side walls so that in the long run the spring will no longer slide smoothly. Moreover, the wiper is situated at the end of a rather long spring, so that a possible small clearance at the area of the guide results in a relatively large displacement of the wiper.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

7 FIGS. 1 and 2 are a longitudinal and a cross-sectional view, respectively, of an embodiment of a device according to the invention,

FIG. 3 is a perspective view ofa detail of the same device on a large scale,

FIGS. 4 and 5 are a longitudinal and a cross-sectional view, respectively, of another portion of the same device, likewise on a large scale, and

FIGS. 6 and 7 are a front and a sectional view, respectively, of another portion of the same device, also on a large scale.

The potentiometer shown in FIGS. 1 and 2 has a trough-shaped housing 1 of synthetic resin, in which a transport screw spindle 3, one end of which may be provided with a drive gear wheel 5, is located in a rotatable manner. For this purpose, the screw spindle 3 has a conically increasing thickened portion 7 at one end (the right-hand end in FIG. 1), the conical portion of which is situated in a likewise conical cavity 8 in a plate 9 (see also FIGS. 6 and 7). The plate 9 is L-shaped and also serves as an electrical connection to a contact pin 11 provided in the bottom of the trough 1. The plate 9 can be displaced in a resilient-manner in the direction of the axis of the screw spindle 3, and also is provided with a slot 12 extending from the cavity 8 to the upper edge of the plate, the width of this slot being between the thickness of the thickened portion 7 on the screw spindle 3 and that of the adjoining thinner portion of the screw spindle.

The left-hand end wall of the housing 1 has a similar cavity and slot, in which a likewise conically increasing thickened portion of the screw spindle 3 fits. The screw spindle 3 can thus be very readily mounted in the housing 1 by pushing the plate 9 to the left, for example, by means of a tool, by subsequently lowering the screw spindle into the slot 12 and the corresponding slot in the left-hand end wall, and finally by releasing the plate towards the right, so that the conical portions of the thickened portions at the ends of the screw spindle are pulled into the conical cavities of the plate and the lefthand end wall, and remain located in these cavities. The housing 1 can subsequently be closed with a lid 13. In addition to the simplicity and hence the low cost of mounting, this construction also offers the advantage that any axial clearance of the screw spindle 3 is eliminated by the resilience of the plate 9, which considerably enhances the adjusting accuracy and the stability of the potentiometer. I

The transport spindle 3 serves for the rectilinear displacement of a slide 15 (see also FIGS. 4 and 5) having a contact spring 17 (see also FIG. 3). The slide 15 is guided by the inner walls of the trough l and by two ridges 19 formed on these inner walls. The contact spring 17 comprises two portions, i.e., a nut portion 21 and a wiper portion 23. Both portions are formed by a mainly vee-shaped leaf spring, the openings of the vees of said leaf springs facing each other, so that a side elevation of the contact spring 17 is approximately diamond-shaped. In order to obtain a considerable rigidity in the longitudinal direction, i.e., direction of transport it is desirable to have a rather large angle between the limbs of the vee, for example, The tip of the vee of the nut portion 21 of the contact spring 17 engages the screw thread of the transport screw spindle 3. In order to ensure that, in spite of the said large angle between the limbs of the vee, the tip is firmly held in the screw thread, the limbs of the vee-shaped nut portion 21 are preferably bent near the tip such that the angle between the portions of the limbs engaging the screw thread is considerably sharper than that between the portions of the limbs which are situated farther from the tip.

The wiper portion 23 of the contact spring 17 preferably comprises, over a substantial portion of its length, considerably less material per unit of length than the nut portion 21. In the embodiment shown in FIG. 3, this is achieved by longitudinally dividing the wiper portion 23 into two portions, over the largest portion of its length, by an elongated aperture 25, which extends from a point near the end of one limb via the tip of the vee to a point near the end of the other limb. However, other ways of achieving this object are also possible, for example, by making the wiper portion 23 narrower or thinner than the nut portion 21. The advantage of the method used here, however, is that not only the leaf spring constituting the wiper portion 23 is rendered more flexible, but that also the actual wiper is divided into two parts. As already mentioned, greater flexibility of the wiper portion 23 is desirable so as to ensure that the nut portion 21 always keeps the slide 15 pressed onto the ridges 19 so that actually two independent spring systems are produced, i.e., at one end the nut portion 21 pressing the slide 15 and, at the other end the wiper portion 23 pressing the actual wiper against a resistance track 27 situated on the bottom of the trough 1. This resistance track 27' may be formed, for example, by a carbon layer. In particular in that case it is desirable that the wiper is divided into two parts in order to ensure proper contact in any position of the slide. As is shown in FIG. 3, the wiper portion 23 may be shaped such that the tip of the vee is rounded off so that the wiper travels over the resistance track 27 more smoothly and with a larger contact area.

At the area where both portions of the contact spring 17 touch each other, the limbs of the vees are bent, so that the diamond has two diagonally opposed, stripshaped protrusions 29 which are co linear with its longest dimension and parallel to the direction of travel of the slide. Via these protrusions 29 the contact spring bears on two bridges 31 at the ends of the slide 15 under a downward pressure, said bridges connecting the side walls 33 of the slide 15 to each other (see FIGS. 4 and The slide bears on the ridges 19 in a manner such that it cannot be tilted, and the comparatively wide strip-shaped protrusions 29 bear under spring pressure on the bridges 31 in a manner such that they cannot be tilted, Consequently, when the spindle 3 is rotated, the nut portion 21 cannot be tilted so that this possibility of clearance in the drive of the slide 15 is eliminated.

As is shown in FIG. 3, the contact spring 17 can be formed from a long strip of resilient material which is given the correct shape after which it is folded double, the crease in this case coinciding with the end of the left-hand protrusion of the two protrusions 29. It is equally possible, however, to manufacture both portions 21 and 23 of the contact spring 17 separately, and to place them loosely on top of each other or to join them, for example, by spot welding. In that case the rigidity of the nut portion 21 can also be increased by choosing for this portion a material other than that for the wiper portion 23.

What is claimed is:

I. A potentiometer comprising a trough-shaped housing, a resistance track carried within said housing, a slide movably arranged over said resistance track, a contact spring carried by said slide, said slide carrying said spring being rectilinearly displaceable and guided by inner walls of said trough-shaped housing and by ridges provided thereon, a transport screw spindle mounted within said housing for causing rectilinear dis placement of said slide and spring upon rotation thereof, a first portion of said contact spring in engagement with said screw thread acting as a nut and an elec trical contact, a second portion of said contact spring forming a wiper which is movable over said resistance track, each of said portions of said contact spring forming a substantially vee-shaped leaf spring having stripshaped ends, the openings of said leaf springs facing each other so that when viewed in a side elevation said contact spring is diamond-shaped the longest dimension of which extends in the direction of said slide, the strip-shaped ends of said nut portion pressing said slide against the guide ridges of said housing, and the tip of said vee of the wiper portion of said contact spring engaging said resistance track with a force smaller than that exerted by the nut portion on the screw spindle.

2. A potentiometer as claimed in claim 1, wherein the wiper portion comprises considerably less material per unit of length over a substantial portion of its length than the nut portion, the tip of the vee of which engages the said screw thread.

3. A potentiometer as claimed in claim 1, wherein the wiper portion is longitudinally divided into two parts over the largest portion of its length by an elongated aperture extending from a point near the end of one limb via the tip of the vee to a point near the end of the other limb.

4. A potentiometer as claimed in claim 1, wherein the transport screw spindle is provided at at least one end with a conically increasing thickened portion, this end being located in the housing in that the conical portion of the thickened portion is situated in a likewise conical cavity in a plate which is resilient in the axial direction of the screw spindle, a slot which starts at the edge of the plate terminating in said cavity, the width of said slot being between the thickness of the said thickened portion on the screw spindle and that of the adjoining thinner portion of the screw spindle. 

1. A potentiometer comprising a trough-shaped housing, a resistance track carried within said housing, a slide movably arranged over said resistance track, a contact spring carried by said slide, said slide carrying said spring being rectilinearly displaceable and guided by inner walls of said trough-shaped housing and by ridges provided thereon, a transport screw spindle mounted within said housing for causing rectilinear displacement of said slide and spring upon rotation thereof, a first portion of said contact spring in engagement with said screw thread acting as a nut and an electrical contact, a secoNd portion of said contact spring forming a wiper which is movable over said resistance track, each of said portions of said contact spring forming a substantially vee-shaped leaf spring having stripshaped ends, the openings of said leaf springs facing each other so that when viewed in a side elevation said contact spring is diamond-shaped the longest dimension of which extends in the direction of said slide, the strip-shaped ends of said nut portion pressing said slide against the guide ridges of said housing, and the tip of said vee of the wiper portion of said contact spring engaging said resistance track with a force smaller than that exerted by the nut portion on the screw spindle.
 2. A potentiometer as claimed in claim 1, wherein the wiper portion comprises considerably less material per unit of length over a substantial portion of its length than the nut portion, the tip of the vee of which engages the said screw thread.
 3. A potentiometer as claimed in claim 1, wherein the wiper portion is longitudinally divided into two parts over the largest portion of its length by an elongated aperture extending from a point near the end of one limb via the tip of the vee to a point near the end of the other limb.
 4. A potentiometer as claimed in claim 1, wherein the transport screw spindle is provided at at least one end with a conically increasing thickened portion, this end being located in the housing in that the conical portion of the thickened portion is situated in a likewise conical cavity in a plate which is resilient in the axial direction of the screw spindle, a slot which starts at the edge of the plate terminating in said cavity, the width of said slot being between the thickness of the said thickened portion on the screw spindle and that of the adjoining thinner portion of the screw spindle. 